Conventionally, in surveys of underwater states using an unmanned underwater vehicle submerged underwater, it has been necessary to move the underwater vehicle on a mother ship to the vicinity of a survey point and lift down the underwater vehicle, or to cause the unmanned underwater vehicle to travel by itself from a waterside location to the survey point. Moreover, since radio waves attenuate significantly underwater, it is common practice to use wired communication to transmit and receive signals to and from the underwater vehicle.
Conventionally, small-size unmanned aerial vehicles (UAVs) represented by industrial unmanned helicopters have been difficult to obtain due to their expensive airframes. Moreover, stable flight of unmanned aerial vehicles requires skillful operations. In recent years, however, airframe components such as acceleration sensors and angular velocity sensors have been improved in performance and lowered in cost. Moreover, much of the operation for controlling the airframe has been automated, which has led to significant improvements in the operability of the airframe. In light of the circumstances, attempts are currently being made to expand the application of multi-copters, in particular small-size multi-copters, over and above recreational purposes, to various missions in a broad range of areas.